The present invention relates to a method for protecting equipment and switching functionality in a telecommunication system, which system comprises a central processor and regional processors, one or more of which is/are standby processor(s).
The invention also relates to a system for protecting such equipment and switching functionality.
Within a switching system there is a requirement that no more than 32 traffic devices are allowed to be affected by a single fault (equipment fault or transmission fault).
When PCM systems with higher bit rates (above 2 Mbit/s) are being terminated in the telephone exchange, equipment protection and protection switching are required in order to fulfil the requirement above. Equipment protection is also needed for other types of equipment which control more than 32 traffic devices, e.g. signalling terminals, Access Unit, boards, etc. This means that for the equipment there must exist a standby unit that can take over in case of failure.
The Protection Switching mechanisms are specified in references 2-9.
With the existing information models in Ericsson""s digital telephone exchange AXE, introducing Equipment Protection and Protection Switching causes a number of problems:
How to connect/define the working and standby equipment?
How to notify the operator when protection switching occurs?
How do we know that the protection mechanisms work?
How do we know which equipment is active and which is standby?
How do we initiate/terminate the protection switching capability?
How do we perform manual switching?
How to handle the traffic devices?
And a number of other problems.
In FIG. 1 there is illustrated schematically a printed principle of an existing information model.
In the model illustrated in FIG. 1, the EM is the representation of the hardware as seen from the control system (Central Processor and Regional Processors). The SNT is the representation of the hardware as seen from the xe2x80x9capplication systemxe2x80x9d.
A Device is a data record containing data representing a call.
DIP is an information element representing the transmission. Only equipment that have a line interface (transmission interface) have a DIP connected.
The invention introduces a new concept xe2x80x9cProtection Groupxe2x80x9d into the information model in order to control the Equipment Protection and Protection Switching functionality.
Known Solutions
There have been presented some ideas of using the existing information model in order to control the Equipment Protection and Protection Switching function.
For example the devices are connected to an SNT as before. In addition a new SNT is defined that is supposed to take over the control in case of a failure, see FIG. 2 which illustrates a protection introduced at SNT level.
One of the problems with such prior art solutions is that the system configuration set by command is changed if protection switching occur.
In case of a protection switch the devices are connected to another SNT than originally connected to by command.
It is also very difficult to see which equipment is standby or active, and also difficult to see which equipment forms a protected pair.
In addition this solution causes a mixing of functionality on SNT level since the SNTs must also contain the protection mechanisms.
With this solution it is also very difficult to make a flexible concept that allows different types of protection switching methods, e.g. 1+1 protection or 1:n protection
Further Prior Art
WO95/10146 (Opoczynski/ADC Telecommunications Inc.) relates to backup equipment which will come into operation if a failure should occur in a telecommunication system. A central processor is used for monitoring the status of a plurality of pairs of telecommunication modules, each pair having an operating module and a standby module. Upon failure the central processor signals to a standby module, which orders switching of all modules being involved, in case a standby module is activated.
WO95/224803 (Madonna et al./Excel, Inc.) discloses a programmable telecommunication switch with automatic backup of line cards which provide complete redundance, namely including multiple I/O busses, standby I/O card and standby line card.
WO95/29544 (Li et al./Cisco Systems, Inc.) relates to a system and a protocol for routing data packets from a host on a LAN by means of a virtual address belonging to a plurality of routings. If one of the routers becomes inoperative, a standby router will emulate a new router.
U.S. Pat. No. 5,014,261 (Masahiro et al./Fujitsu Limited) discloses a switching system for switching a unit or a plurality of units which are in a first working condition, to one or a plurality of units which are in a standby condition. Upon failure in one or more of the working units, this unit or units will automatically be connected to a common standby unit.
GB 2 294 613 (Bruce/Northern Telecom Limited) discloses a telesystem comprising multiplexed lines, and in order to avoid the problem of having separate line controllers, it is suggested that each tributary channel has an interface towards the multiplexers via a protecting unit, which can switch the tributaries between a first multiplexer and a second multiplexer when the performance of the system using said first operation multiplexer has been degraded.
However, none of these publications give any instructions for a new xe2x80x9cprotection groupxe2x80x9d concept, namely to introduce such a protection group between existing clients (devices) and the level of servers (SNT level).
The idea of the present invention is to introduce a new concept, here called xe2x80x9cProtection Groupxe2x80x9d, that controls the protection switching mechanisms.
The idea is to introduce the Protection Group between the existing client and server layers in order to protect the client(s) from faults at the server layer.
The Protection Group controls the configuration on server layer with respect to protection mechanisms. This means that the Protection Group administrates which server units should be working (active) and which should be standby units.
At the server layer the different server units have their own working state as before, and the units do not have any information about configurations for protection mechanisms.
In case of a fault on server layer, this is reported to the Protection Group, which then decides whether to switch to a standby unit or to inform the client that a fault has occurred (i.e. request a blocking of the client).
In other words, in connection with a method as stated in the preamble, such a method is according to the invention characterized by introducing a protection group between the existing client(s) and server layers (i.e. switching network terminals), said protection group administering which server units should be working (active) and which should be standby units.
The method may appropriately be implemented when said method comprises the use of a protection group which communicates both with the server(s) (i.e. switching network terminals) and the client(s) or device(s) in question, and which protection group in case of a fault on server layer decides whether to switch to a standby unit or to inform a client that a fault has occurred (i.e. requesting blocking of client).
A system for protecting equipment and switching functionality in a telecommunication system, which system comprises a central processor and regional processes, one or more of which is/are standby processor(s), will accordingly, according to the present invention be characterized in that said system comprises a protection group means introduced between the existing client(s) and server layers (i.e. switching network terminals), said protecting group comprising means for administering which server units should be working (active) and which should be standby units.
Further features and advantages of the present invention will appear from the following description taken in connection with the enclosed drawings, as well as from the appending patent claims.